Conventionally, in most stores and plants, sales management of goods and production control of products are carried out by attaching bar codes representing digital information to articles and optically scanning the bar codes to read the information. Generally, for a bar code of this type, information is read from the combination of detected signals obtained by casting a light beam to the bar code and photoelectrically converting the intensity of its return light.
The reading system for information based on a bar code of this type will now be described with reference to the conceptual view of FIG. 21. A light beam from a light-emitting device 501 is narrowed by a light-emitting lens 503 and this light beam is reflected by a mirror 507 of a scanning mirror (moving mirror) 505 so as to be incident on a bar code 509. The mirror 507 swings to cast the light beam to the entire range of the bar code 509. The mirror 507 is caused to swing about a swing center shaft 515 as supporting shaft, by inserting a magnet 511 attached to the mirror 507 into a driving coil 513 and then causing a positive/negative current to flow through the driving coil 513, for example, in a predetermined cycle.
The light cast on the surface of the bar code 509 is irregularly reflected but returns to the mirror 507 with changes in the quantity of light due to the black and white of the bar code. The light beam reflected by the mirror 507 is then condensed by a condensing mirror 517 and the changes in the quantity of light are electrically converted and thus outputted by a light-receiving device 519.
To improve the reading accuracy, a band-pass filter (BPF) 521 is provided on the front side of the light-receiving device 519 to prevent intake of unwanted light beams having a frequency other than the emission frequency.
Such a reading system is implemented by a bar code reading apparatus shown in FIG. 22. This bar code reading apparatus has a light-emitting mechanism A constituted by the light-emitting device 501 and the light-emitting lens 503 which are housed in a housing 525, and a light-receiving mechanism B constituted by the light-receiving device 519, the light-receiving lens 517 and the BPF 521 which are housed in a housing 527, with the light-emitting mechanism A and the light-receiving mechanism B mounted on a board 529, as shown in FIG. 22.
The electric connection within the respective housings 525, 527 is made by wire bonding or the like. The mirror 507 of the moving mirror 505 is arranged so that it can swing about the swing center shaft 515. These light-emitting mechanism A, light-receiving mechanism B and the moving mirror 505 are arranged within a frame, not shown, to constitute the bar code reading apparatus.
In the bar code reading apparatus constituted as described above, the light-emitting mechanism A and the light-receiving mechanism B are housed in separate casings. That is, the bar code reading apparatus has a double-armor structure. Therefore, miniaturization of the bar code reading apparatus is limited and may cause deterioration in the light-receiving accuracy and uncertainty of the swing of the mirror.
Particularly, in a handy-type bar code reading apparatus, since no magnetic force is applied to the moving mirror when the power is off, there arises a problem that the moving mirror can freely swing and its inertial force may cause the mirror to be abutted against the peripheral members. Generally, the mirror of the moving mirror is formed in a rectangular shape by using a glass material, and the edge surface of the mirror made of the glass material is fragile. Therefore, when a particularly strong shock is applied, for example, when the bar code reading apparatus is dropped by accident, the sharp and fragile edge part and four corners might be damaged in contact with the peripheral members.
As a solution to such a problem, the moving mirror for the conventional bar code reading apparatus is constituted by bonding a dedicated buffer member such as a cushion sheet 533 to a protective stopper member 531 shown in FIG. 22, thus preventing the damage of the mirror 507 due to the contact with the peripheral members. However, as the separate buffer member is bonded, the reduction in size and weight is obstructed and the manufacturing cost is increased. Moreover, the work performance is not very good because the buffer member must be bonded to the very small protective stopper member.
In the conventional bar code reading apparatus, the resonance frequency of the swing mechanism (including the mirror 507) which swings about the swing center shaft 515 is decided by adding an elastic member such as a leaf spring or silicone to the part of the mirror 507 of the moving mirror 505 which in contact with the swing center shaft 515.
In manufacturing the bar code reading apparatus, there may be some difference in the dimension and weight of the components, which causes difference in the resonance frequency of the swing mechanism on completion of the assembly of the apparatus. Therefore, a desired resonance frequency may not be provided. Moreover, there is also a problem that the static posture of the mirror 507 when the driving coil 513 is not electrified (neutral point of the mirror when swinging) might differ because of the difference in the relative position between the mirror 507 and the swing center shaft 515 and the mounting position of the magnet 511.